1. Technical Field
The present disclosure relates to a communication device and a communication method which perform communication using electric field coupling.
2. Related Art
In general, RFID (Radio Frequency IDentification), infrared communication, and short-range radio communication schemes besides wired communication for a system having a communication device are known. Since non-contact communication by radio waves or the like is possible, the non-contact communication is utilized in various places, for example, such as an event site and a station ticket gate.
On the other hand, since devices using radio waves are regulated by law and are easily affected by interference or obstruction from peripheral devices, the techniques of new communication schemes using electric field coupling have been disclosed (for example, see Japanese Patent No. 407-4661 and Japanese Unexamined Patent Application Publication No. 2004-153708). When a human body is used for a signal transmission path, external leaking may be difficult as compared to radio waves or the like, and the performance of communication may be improved by control of an output level of a transmission signal.
However, even though the communication scheme uses the above-described electric field coupling, the communication performance thereof is affected by environmental noise (external noise generated by a peripheral device, noise of a power supply system, or the like). When a noise level is high, a transmission signal may be buried in the environmental noise. Therefore, there is a problem in that communication performance may be degraded.
In this case, an output level of the transmission signal may be set to be higher than the noise level. However, when the output level is set to be high, there is a problem in that a radiated electric field becomes excessively strong and communication is performed even though it is not immediately before a human body is in contact with a receiver, or a transmitter and a receiver directly communicate beyond the human body, thereby establishing communication without passing through the human body in spite of the human body being used for a signal transmission path.
In the case where the transmitter is a portable device which is driven by a battery, there is a problem in that the battery life is shortened when the output level of the transmission signal is set to be simply high.
Here, in terms of solutions of these problems, it should be noted that the human body itself is affected by environmental noise. This is because the human body itself which is the signal transmission path functions as an antenna and easily picks up the environmental noise.
That is, when the environmental noise received by the human body is not recognized, the improvement of true communication performance may not be achieved even though it is possible to set an output level of a transmission signal on the basis of a noise level.